Tuesday, April 7, 2009

Palo Verde Trees

Native to the Sonoran desert, palo verde trees are easily recognized by the greenish bark of their secondary branches and twigs. Barren looking for much of the year, the trees produce brilliant yellow flowers in spring and small, compound leaves develop on the terminal branches from mid summer into mid autumn. Since the green branches and twigs are capable of photosynthesis, the leaves are often dropped early if prolonged drought occurs; in fact, these trees are also capable of shedding their terminal branches in order to conserve water. Palo verdes are also equipped with deep tap roots, which obtain water from below and serve as anchors during flash floods.

Two species of palo verde are found in the Sonoran. The blue palo verde, Arizona's State Tree, grows to forty feet; favoring lower terrain along washes, this species is commonly planted as an ornamental due to its showy flowers and attractive blue-green stems. The yellow palo verde, found in foothills to 4000 feet, is a shrubby tree with yellow-green branches; hardier than its larger cousin, it may live for hundreds of years. Both species, though often despised for their seasonal shedding of leaves, stems and seed pods, are important members of the Sonoran Desert ecosystem, providing vital shade for developing saguaros.

Members of the legume family, which also includes locusts, acacias, redbuds, mimosas and mesquite, palo verdes produce copious seed pods, a favored food of javelinas and many desert rodents. Their leaves and terminal twigs are browsed by deer, desert bighorn sheep and jackrabbits while their abundant flowers provide nectar for hummingbirds, bees and other insects.